Sound based fire alarm system and method

ABSTRACT

Stovetop fires are among the more prevalent of resident fire hazards and smoke detectors are among the most prevalent and economical forms of residential fire alarms. Automatic stovetop fire extinguishers can prevent property damage and even personal injury; however, these stovetop fire extinguishers may also limit smoke emissions and the subsequent detection of smoke. While an initial fire may be efficiently subdued by an automatic stovetop fire extinguisher, it is often desirable to alert present and future occupants of a fire hazardous condition. A sound based fire alarm system and method are described herein, which detects a sound burst emitted upon deployment of an automatic stovetop fire extinguisher and triggers a continuous fire alarm to alert occupants of a potentially fire hazardous condition. Alarm signals can be audible, visual, or both. The system may be a stand alone system and use battery power for affordability and ease of installation. The method described herein enables the ready and automatic extinguishment of a stovetop fire, while alerting those in the surrounding area or those in adjacent dwellings of a fire situation.

CROSS REFERENCE TO RELATED PATENTS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/240,081, filed Sep. 29, 2008, which is incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a fire alarm system and method, andmore particularly to a sound based fire detection and fire alarm system.

Conventional fire alarm systems are frequently part of a conventionalhome security system. Security sensors include motion detectors, whileconventional fire sensors include smoke detectors and heat detectors.The home security system typically has a control panel, which receivessensor input and sends sensor commands. In addition to sensors, the homesecurity system may comprise various warning lights, horns, bells andthe like. These home fire and security systems add significant costs tothe home and may be found in large homes or higher priced homes.Surveillance and monitoring service may also be incorporated into a fireand security system at an additional recurring service expense.

Conventional self contained smoke detectors are less expensive thesystems referenced supra and are common in residential dwellings and maybe required for insurance purposes. These battery operated units detectsmoke via various means and provide a loud alert for occupants whensmoke is detected. Smoke detectors are often positioned away from thecooking area to avoid nuisance alarms. Other conventional fire detectorssense heat but are less common. Commercial buildings may use selfcontained smoke detectors, a fire and security system, or a combinationof both.

Stovetop fires, in particular, are a well known residential andcommercial hazard. An unattended stovetop fire, for example a greasefire, can cause damage to nearby appliances and cabinets. Worse,stovetop fires can lead to structural damage or personal injury. Becausethe propensity for stovetop fires is so pervasive, an efficient means ofautomatic fire suppression is desired. Even if a stovetop fire isattended, an automatic extinguishing method may be more effective andexpedient compared to manual means.

There are a number of conventional fire extinguishing systems, toinclude automatic stovetop fire extinguishers. Conventional fireextinguishers include, for example, the automatic stovetop fireextinguisher taught by Williams, U.S. Pat. No. 5,518,075. The unit canbe readily mounted over a stovetop and upon detection of flames, theextinguisher releases a fire suppressant. While release of firesuppressant may extinguish a current fire, a smoke alarm, as aconsequence, may not be triggered to alert occupants of the presentdeployment of fire suppressant and any potential for subsequentadditional fires. To avoid an unwarranted smoke alarm trigger, theconventional smoke alarm in a typical residence is not placed near thecooking area. This typical proximity may decrease the likelihood of thesmoke detector triggering upon activation of a distant automaticstovetop fire extinguisher.

It would be desirable to provide an automatic fire extinguisher and firealarm system which suppressed any present flames while alerting buildingoccupants of the hazardous situation. Depending on the applicable firecode, the building environment, and building residents themselves, afire system may be required to have both extinguishment and alertfunctions. As, an example, it may desirable or required by fire codes toalert the neighboring apartments or dorm rooms of a fire hazardcondition in an adjacent dwelling. For a multitude of situations, itwould be desirable to provide an efficient and economical stovetop fireextinguisher and fire alert system.

SUMMARY OF THE INVENTION

The present invention provides an audible fire alarm upon deployment ofan automatic fire extinguisher. Aspects of the present invention providebelow are neither exhaustive nor exclusive.

An aspect of the present invention is to provide a continuing alarm inconjunction with automatic stovetop fire suppression system. Anotheraspect of the present invention is to provide a continuous audible alertfor occupants of a dwelling or commercial building upon the automaticrelease of a fire suppressant and/or to provide a continuing audiosignal warning those present or those subsequently entering a buildingof a possible fire hazardous condition.

Another aspect of the present invention is to forward the alert signalto neighbor UL rated smoke detectors, which in turn sound an alarm.

Another aspect of the present invention is to trigger a fire alarm uponsensing of a brief high decibel signal.

Another aspect of the present invention is to provide a continuousaudible alarm upon activation of a STOVETOP FIRESTOP® fire suppressor(Williams-Pyro, Inc., Fort Worth, Tex., USA).

Another aspect of the present invention is upon extinguishing of a localfire, to visually notify remote occupants of the hazardous situation inthe building.

Another aspect of the present invention is to interface withself-contained fire extinguishers and self-contained smoke detectors toprovide a continuing audible alarm to occupants throughout a buildingupon the deployment of a local automatic fire extinguisher.

Another aspect of the present invention is to provide a continuousaudible signal to residents of a stovetop fire condition, to includeresidents who are remote from the stovetop or sleeping.

Another aspect of the present invention is that it enables a sound basedfire detector to be incorporated into an existing fire control system.

Another aspect of the present invention is to provide a continuing audiosignal warning those present or those entering a building of a possiblefire hazardous condition.

Another aspect of the present invention is to provide an affordablesound based fire alarm system, which provides a continuous audible alarmsignal to alert residents of a stovetop fire condition and whichoperates via a self-contained power supply.

Embodiments of the present invention may employ any or all of theexemplary aspects above. Those skilled in the art will furtherappreciate the above-noted features and advantages of the inventiontogether with other important aspects thereof upon reading the detaileddescription that follows in conjunction with the drawings.

BRIEF DESCRIPTION OF THE FIGURES

For more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures, wherein:

FIGS. 1A-1B shows a sound based fire alarm system employed near astovetop and a sound based fire alarm block diagram, respectively, inaccordance with an exemplary embodiment of the present invention;

FIG. 2 shows a block diagram of a sound based fire alarm, to includeinter-connections of system components, in accordance with an exemplaryembodiments of the present invention;

FIG. 3 shows a block diagram of a sound based audible fire alarm systememploying different alarm devices, in accordance with exemplaryembodiments of the present invention;

FIG. 4 shows a block diagram of a sound based audible fire alarm systemincorporating communication between stand alone United Laboratories (UL)rated smoke detectors, in accordance with an embodiment of the presentinvention;

FIG. 5 shows an exemplary method of providing a sound based fire alarmsystem, in accordance with an embodiment of the present invention;

FIG. 6 shows an exemplary recording of an audible emission from anautomatic stovetop fire extinguisher in accordance with the presentinvention;

FIG. 7A shows a filtered exemplary recording of the audible emission ofFIG. 6 filtered by a four point moving average to halve the noise, inaccordance with the present invention; and

FIG. 7B shows a normalized power spectral density of a recorded audibleblast from a stovetop fire extinguisher, in accordance with an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention, as defined by the claims, may be better understood byreference to the following detailed description. The description ismeant to be read with reference to the figures contained herein. Thisdetailed description relates to examples of the claimed subject matterfor illustrative purposes, and is in no way meant to limit the scope ofthe invention. The specific aspects and embodiments discussed herein aremerely illustrative of ways to make and use the invention, and do notlimit the scope of the invention.

FIG. 1A shows a sound based fire alarm system employed near a stovetop,in accordance with an exemplary embodiment of the present invention. Anautomatic stovetop fire extinguisher 102 is mounted above a stovetop105. Mounted on a nearby wall is a sound based fire alarm unit 110. FIG.1B shows a block diagram of a sound based fire alarm system 110, inaccordance with an embodiment of the present invention. The sound basedfire alarm system 110 comprises a sensor 112, sensor circuitry 120,control circuitry 140, alarm circuitry 160, and an alarm indicator 180.In the particular embodiment of FIG. 1B, the alarm indicator 180 isprovided by a speaker. Additional and/or alternative alarm indicatorsare discussed below with reference to FIG. 3. In accordance withembodiments of the present invention, sensor 112 is a microphone.Different embodiments of the present invention employ differentmicrophone types. A measurement, or condenser, microphone provides anoutput signal corresponding to the sound pressure level of the sensedsignal. The present invention may be readily employed with an automaticstovetop fire extinguisher 102, for example a STOVETOP FIRESTOP(Williams-Pyro, Inc., Fort Worth, Tex., U.S.A). As described in U.S.patent application Ser. No. 12/240,081, referenced above, a near 140decibel burst is emitted upon ignition of the black powder substitutepropellant comprised in a STOVETOP FIRESTOP fire suppressor. By placinga sound based fire alarm 110 in the vicinity of automatic firesuppressor 102, sensor 112 will sense the near 140 decibel burst if theautomatic fire extinguisher deploys. Distinction of ambient sounds fromthe sound burst generated by the automatic stovetop fire extinguisher isperformed before triggering of the sound based fire alarm, whichprovides a continuous alarm signal to occupants.

In an alternate embodiment a diffuse field measurement microphone, whichmeasures sound waves from all directions, is employed as the soundsensor 112. A desirable diffuse field microphone, for use in the presentinvention, has a dynamic range comparable to the signature powerspectral density of the fire suppressor's sound emission. According toan exemplary embodiment, the microphone has a maximum sound pressurelevel of at least 150 decibels and a frequency response spanning thenarrow bandwidth of the fire suppressor's sound emission frequency, asshown for example in FIGS. 7A and 7B. In yet another embodiment, a nearfield microphone is employed in a sound based fire alarm system. Nearfield microphones are particularly suited for embodiments which enablemounting of the sound based alarm 110, or just the sensor 112, near thestovetop area 106, and more particularly, near the stovetop fireextinguisher 102.

FIG. 2 shows a block diagram of a sound based fire alarm system, inaccordance with an embodiment of the present invention. Sound sensor212, microphone, is electrically connected to sensor circuitry 220.According to the embodiment of FIG. 2, a battery power supply isprovided within sensor circuitry 220. Battery power supply 222 providesa number of desirable aspects, which include a stand alone system,affordability and ready incorporation into an existing automaticstovetop fire suppression system. Sensor circuitry 220 includes a filter224 and may include an amplifier 223. In accordance with anotherexemplary embodiment, sensor circuitry 220 and sensor 212 are containedin a same housing. In alternate embodiments, amplification and filteringof sound waves may be accomplished using circuitry within a microphonehousing. In still another embodiment, a microphone sensor 212 isaccessorized with a digital signal output proportional to a soundpressure level in decibels or nepers. The output of the sensor circuitryis electrically connected to control circuitry 240.

Control circuitry 240 determines the presence of a deployed stovetopfire extinguisher from the output of the sensor circuitry 220. Inaccordance with an exemplary embodiment, logic circuitry 241, amicrocontroller 242, or a combination of both can be used to detect thesound emission of a deployed stovetop fire extinguisher. Any of a numberof signal characteristics may be assessed and compared to a thresholdvalue corresponding to the audio signal generated upon deployment of anautomatic stovetop fire extinguisher. In accordance with an exemplaryembodiment, a condenser instrument microphone is mounted beneath an overthe stovetop microwave 103, as shown in FIG. 1A, near an automaticstovetop fire extinguisher 102. A decibel reading in excess of 110decibels at a frequency greater than 2.5 kHz meets thresholdrequirements for determination of a deployed stovetop fire extinguisher.In still another embodiment, a sound pressure level in excess of 125decibels at any frequency for a duration of at least 5 milliseconds willexceed threshold requirements and determine the presence of a sonicsignal from an activated stovetop fire extinguisher. The above soniccharacteristics for determination of a deployed stovetop fireextinguisher are exemplary. These sound characteristic quantitiesdescribed above, as measured near a stovetop, may avoid falsedeterminations of an activated stovetop fire extinguisher as compared tosounds sensed from background noises.¹ A microphone signal picked upduring activation of an automatic stovetop fire suppressor is shown inFIG. 6 and is further described below with reference to the same.

Referring to FIG. 2, in still other embodiments, when a control panelfor a fire and security system is present, the output of the controlcircuitry may interface directly with an existing control panel 243.Communication 245 may be conducted, for example, by an RS485 cable. Instill other embodiments, the control circuitry 240 comprises atransceiver 247, and a wireless radio frequency trigger signal istransmitted via a transceiver in the control circuitry and received atthe control panel via a receiver 248, as shown for example, in FIG. 2.Control circuitry 240 can be housed within a sensor circuitry housingand may be driven from a common battery supply 222 or from its ownbattery supply 249.

Control circuitry 240 connects to alarm circuitry 260, which in turndrives a fire alarm to generate a continuous alarm signal. FIG. 3 showsa block diagram of a sound based fire alarm with a number of alarmcircuitries 360, in accordance with embodiments of the presentinvention. Sound sensor 312 is electrically connected to sensorcircuitry 320, which connects to control circuitry 340. The output ofthe control circuitry 340 is electrically coupled 359 to an alarmcircuitry 360-2, which in turn drives an alarm 380. Each of thecircuitries, 320, 340, 360 may be housed in a same housing, inindividual housings, or in some combination. Similarly the sensor 312and alarm, for example 380, may be housed with its respective circuitryor separately, as needed or as desired. In still other embodiments atleast one alarm circuitry and alarm device are remote from the controlcircuitry and/or the sensor circuitry. As shown in FIG. 3, the controlcircuitry may connect to different alarm types 380-1 to 380-4, whereeach alarm has its own alarm circuitry 360-1-360-4. Alarm devices mayinclude a smoke detector 380-3, a buzzer 380-1, a piezoelectric buzzer380-4, a speaker 380-2, or a strobe light, not shown. Each alarmcircuitry may comprise a battery power supply 363 supporting anindependent stand alone system. Different embodiments of a sound basedfire alarm 310 may comprise any combination of alarm devices.

In accordance with one exemplary embodiment, a tone generator 362-2provides the alarm signal which is amplified and drives speaker 380-2. Acommercially available microprocessor-based digital tone generator maybe employed, or a simpler transistor-transistor logic (TTL) timer-basedtone generator may be employed. For some applications, such as amulti-resident or multi-dwelling building, a digital multi-tone tonegenerator, such as PRONOR NV's Digital Multi-tone Tone Generator V-9927A(PRONOR NV, Gent, Belgium) may be employed. In other embodiments, asound generator integrated circuitry 363-2, an 8/10 W amplifier 364-2,and an 8 ohm speaker 380-2 can provide the alarm circuitry and alarmdevice, respectively.

As appreciated by one of ordinary skill, a single 9 volt battery may beused to supply 9 volts across a speaker or piezoelectric buzzer, while adiode combination or voltage regulator can drop the 9 volts to 5 or lessvolts across, for example, a programmable interface controller (PIC).

In still another embodiment, a smoke detector is incorporated as thealarm device 380-3. An alarm circuitry 360-3, which drives the smokedetector, will tap into the smoke detector circuitry in parallel withthe smoke detection circuitry, ionizing or photoelectric, and will leavethe smoke detection function intact. In alternate embodiments, the smokedetector is dedicated to the sound based fire alarm system and the smokedetection is disabled. A buzzer 380-1, or piezoelectric buzzer 380-4,may also be used as an alarm device in accordance with embodiments ofthe present invention. A miniature ceramic buzzer can provide 80decibels at 10 cm, while a larger one inch diameter piezoelectric buzzercan provide 108 decibel continuous alarm at only 50 mA for voltagesbetween 5 and 15 VDC. A piezo transducer, piezoelectric buzzer, willproduce high volume when driven near its resonant frequency. A suitabledriver circuitry 363 for a piezoelectric transducer 380-4 may comprise,for example, a 555 astable timer. Piezo transducers require a smallcurrent, usually less than 10 mA, so they can be connected directly tothe outputs of many integrated circuitry chips, without amplification.As discussed above, alarm circuitry 360-1 to 360-4 may include a batteryand may also comprise a programmable interface controller (PIC). Alarmcircuitry 360-4 is shown comprising a battery 363 and a driver circuitry362. Any and all alarm circuitries may comprise a battery and/or drivecircuitry.

FIG. 4 shows a block diagram of a sound based audible fire alarm systemapplied in a building in accordance with an embodiment of the presentinvention, wherein wireless communication across UL rated stand alonesmoke detectors is utilized. Sound sensor 412 senses local sounds,sensor circuitry 420 processes the received signals, and controlcircuitry 440 determines the presence of a deployed automatic stovetopfire extinguisher. Upon determination of a deployed stovetop fireextinguisher, a trigger signal 459 is broadcast via a wirelesstransmitter 447. At remote locations, antennas 447-1 to 447-3 receivethe transmitted signal and activate corresponding smoke detectors480-3-1 to 480-3-3 via respective alarm circuitries 460-3-1 to 460-3-3.The mode of communication, for example, radio frequency or Bluetooth,can vary as distance and power requirements dictate or as desired. Inyet another embodiment, antenna 447 sends out a trigger signal 459 andeach remote antenna 447-1, may not only receive the trigger signal butalso transmit a trigger signal 459-2 for reception by additional remotesmoke detectors. In the latter embodiment, alarm circuitries aremodified to forward a trigger signal as well as tap into the smokedetector circuitry to activate the alarm. By hopping from smoke detectorto smoke detector, a greater area can be incorporated into the soundbased fire alarm system. This embodiment may be particularly well suitedin a multi-dwelling setting, such as a dormitory.

Some embodiments of the present invention may be readily incorporatedinto an existing smoke detector system. For example, in one embodiment,an alarm circuitry may have its own housing 260 and 9 volt batterysupply. Such housing may be easily mounted near a smoke detector andconnections with the same easily made.

FIG. 4 shows an automatic stovetop fire suppressor 402 above a stove405, with a sound based fire alarm nearby and smoke detectors upstairsand down the hall. More particularly a sound sensor 412, a sensorcircuitry 420, and a control circuitry 440 are in proximity to thestovetop 405. Remote smoke detectors 480-3-1, 480-3-2, 480-3-3 are shownwith RF transceivers and alarm circuitries 460-3-1, 460-3-2, 460-3-3connected there to respective smoke detectors.

FIG. 5 shows an exemplary method of a sound based fire alarm, inaccordance with an embodiment of the present invention. An automaticstovetop fire extinguisher, STOVETOP FIRESTOP, is mounted above astovetop 510. A microphone is positioned in the stovetop area 515 tosense local sounds 520. Sensed signals are output to a sensor circuitry530, which processes the sensed signals 535 by, for example high passfiltering and digitizing. Processed signals are output to a controlcircuitry 540. A comparison is made between attributes of processedsignals and respective threshold values 545. If the signal does notexceed threshold 547, sensing of stovetop sounds continues 520. If thesignal exceeds threshold values 547, which correspond to the sound burstemitted upon deployment of the stovetop fire extinguisher, then atrigger signal is sent to an alarm circuitry 550. The alarm circuitrydrives the connected alarm to produce a continuous alarm signal 555.

In an alternate embodiment, if the signal exceeds threshold values 547,which correspond to the sound burst emitted upon deployment of thestovetop fire extinguisher, then a trigger signal is sent to a controlpanel 560. In turn, the control panel activates connected continuousalarms. In an alternate embodiment, if the signal exceeds thresholdvalues 547, which correspond to the sound burst emitted upon deploymentof the stovetop fire extinguisher, then a trigger signal is broadcast toremote alarm circuitries 580. Remote alarm circuitries receive thetrigger signal 585 and activate their respective smoke detectors 590.

FIG. 6 shows a digital recording of a high decibel burst, generated uponactivation of an automatic stovetop fire extinguisher, STOVETOPFIRESTOP. More particularly, FIG. 6 shows output voltage from amicrophone, which is sensing the audible blast of an activating STOVETOPFIRESTOP automatic stovetop fire suppressor, as a function of time 640.Shown on the vertical axis, microphone output 621 is shown in volts 620,with time 631 on the horizontal axis in seconds 630. The vertical axisspans −1.2 to 0.8 volts 622, 624. The signal was sampled at 44.1 kHz andis shown from blast onset 632 for an 11.5 millisecond time span. Thehorizontal axis spans the time from blast onset, 0, 632 to just over 11milliseconds 634. As can be seen from the recording 640, the blast dropsoff to one-half peak power between 6.5 and 7.5 milliseconds. Therecorded signal appears to contain high frequency noise.

FIG. 7A shows an exemplary recording of the audible emission of FIG. 6filtered by a four point moving average. The raw microphone outputvoltage sampled at 44.1 kHz is shown filtered with a 4 point movingaverage, for a lowpass filtering near 5.5 kHz. Filtered microphoneoutput 721 is shown in volts 720 as a function of sequential samples (n)730 at a sampling rate of 44.1 kHz, every 2.27×10⁻⁵ seconds. The timespan of FIG. 7A 734 is equal to that of FIG. 6 634, with samples beingtaken at 44.1 kHz. Likewise the output voltage spans a similar rangefrom −1.0 volts 722 to 1.0 volts 724. From the low pass filteredmicrophone output as a function of time expressed in sequential samples(n) 740, a fundamental frequency of the audible stovetop fireextinguisher blast begins to appear.

FIG. 7B shows a power spectral density for a recording of an audibleblast of a stovetop fire extinguisher in accordance with the presentinvention. Using raw voltage data, FIG. 6 and a hamming window, a powerspectral density was calculated and plotted. Microphone output voltssquared as a function of frequency was calculated. The resulting power,volts-squared, was then normalized to a maximum of 1. The normalizedpower is shown as a function of frequency 750. Normalized microphoneoutput power 760 varies from 0 762 to 1.0 764, shown on the verticalaxis. Frequency, shown on the horizontal axis is shown as a decimalfraction of n, where n equals 44.1 kHz 770. The power spectrum is shownfrom 0 hertz, 0n, 772 to 0.5n corresponding to 22.05 kHz 774. Theresulting function 750 shows the largest contribution to signal powerhas a bandwidth centered at approximately 3.8 kHz with a bandwidth ofapproximately 700 Hz. In accordance with an exemplary embodiment of thepresent invention, a band pass filter 224 with cutoffs at 2.5 kHz to 5.0kHz is applied to the sensed signal in the sensor circuitry 220, shownin FIG. 2. In accordance with another exemplary embodiment, sensorcircuitry 220 comprises a band pass filter with cutoffs at 3.2 kHz and4.2 kHz. And in accordance with another embodiment, filtered signals maybe amplified 222 before being output to a control circuitry 240.

While specific alternatives to steps of the invention have beendescribed herein, additional alternatives not specifically disclosed butknown in the art are intended to fall within the scope of the invention.Thus, it is understood that other applications of the present inventionwill be apparent to those skilled in the art upon reading the describedembodiment and after consideration of the appended claims and drawing.

REFERENCE LIST

-   [1] Perr, J. Basic Acoustics and Signal Processing, Sound.    http://www.linuxfocus.org/English/March2003/article271.shtml#271Ifindex3

What is claimed is:
 1. A sound based fire alarm, the system comprising:a self contained automatic stovetop fire extinguisher which emits aaudible signal upon activation; a sound burst sensor which detectsaudible signals and outputs a sense signal to a sensor circuitry;wherein, the sensory circuitry processes received sensed signals andoutputs processed sensed signals to a control circuitry; wherein, thecontrol circuitry receives processed sensed signals from the sensorcircuitry, determines activation of the self contained automaticstovetop fire extinguisher, and outputs a trigger signal to an alarmsystem when activation of the self contained automatic stovetop fireextinguisher is determined; and wherein, the alarm system comprises analarm circuitry and an alarm device, and wherein, when the alarmcircuitry receives the trigger signal from the control circuitry, thealarm device provides a continuous fire alarm; wherein, the sensorycircuitry filters received sensed signal with a 2.5 kHz to 5.0 kHz bandpass filter and outputs filtered sensed signals to the controlcircuitry; wherein, the control circuitry comprises: a digital signalprocessor which calculates a power spectral density via a fast fouriertransform on a received sensed sound burst signal; and an integratorwhich integrates the power spectral density signal over 3.0 kHz to 4.0kHz; and wherein the control circuitry compares the integrated signal toa 120 decibel value and outputs a trigger signal to the alarm circuitrywhen the integrated signal exceeds 120 decibels.